“My team are playing in the cup tonight” - what does “in the cup” mean?

Likely a football tournament, like the F.A. Cup Though I’d expect it to be a bit more specific like “playing in the cup final tonight” or “playing in a cup match”

Probably refers to a sporting event where the winning team gets a trophy

It's a term for a particular tournament or other sports game/match. Without knowing more context, it would be impossible to say to what the speaker was referring. For example: * Stanley Cup: [https://en.wikipedia.org/wiki/Stanley\_Cup](https://en.wikipedia.org/wiki/Stanley_Cup) * Rugby World Cup: [https://en.wikipedia.org/wiki/Rugby\_World\_Cup](https://en.wikipedia.org/wiki/Rugby_World_Cup) * European Rugby Champions Cup: [https://en.wikipedia.org/wiki/European\_Rugby\_Champions\_Cup](https://en.wikipedia.org/wiki/European_Rugby_Champions_Cup) * World Cup: [https://en.wikipedia.org/wiki/FIFA\_World\_Cup](https://en.wikipedia.org/wiki/FIFA_World_Cup)

A sports competition of some sort, where the reward is the cup.

It depends on the context, but, There are two major types of competition in football. "League" and "Cup". In league competitions, teams of a similar rank all play each other, to score points. At the end of the season, the team with the most points is the winner. The teams with the fewest points may be *relegated* to a lower league. An example is the EPL. A cup is a knock-out event. Teams are selected to play each other randomly. The winner continues to the next round. An example is the FA Cup. English Premiership teams play both league games and cup games.

A lot of good answers in here so far but I think it’s important to note that in American English (the NBA Cup and Stanley Cup would be the most salient Cup examples used in AE), it would be: “My team ***is*** playing in the Cup tonight.”

Although hockey has the Stanley Cup, this phrase is more of a soccer(football) expression. For example, in England a team will play in multiple competitions during the season. They’ll play in their domestic league, and domestic cup competitions (League Cup, FA Cup), and some will play in European cup competitions (Champions league for example example). If some says their team is playing in the cup today, it means they have a match in one of the domestic cup competitions today.

In a tournament where they could win a trophy

Correct me if I'm wrong, but isn't it more correct to say you are playing *for* the cup?

A ‘cup’ usually refers to a sports tournament where if you win you knockout your opponent from the tournament and this goes on until there’s only one team remaining.

An example of “a cup” in the way it is being used here is the Stanley Cup which is championship trophy for the winning hockey team in the national hockey league in North America.

"cup" in this context refers to a tournament, usually a championship. Also, small nit pick: it should be "My team is..." instead of "my team are..." As a team is a collective, and therefore singular. There is only one team.